Study Observes Increased Cattle Death Loss Due To Beta Agonists

New research into the use of beta agonists released this week raises concerns about the animal health and welfare of feedlot cattle. The peer-reviewed article, while acknowledging "significant societal benefits" of beta agonist use, describes an increase in death loss of cattle receiving the feed additives.

Two beta agonists have been approved by the FDA for use in feedlot cattle, ractopamine hydrochloride (Optaflexx), manufactured by Elanco Animal Health, and zilpaterol hydrochloride (Zilmax), manufactured by Merck Animal Health.

Lead author Guy H. Loneragan, BVSc, Ph.D., Texas Tech University, and co-authors Daniel U. Thomson, DVM, PhD, Kansas State University and H. Morgan Scott, DVM, PhD, Kansas State University, found that the incidence of death loss among cattle administered beta agonists was 75 to 90 percent greater than cattle not administered the beta agonists.

"This increase in death loss raises critical animal-welfare questions," Loneragan said. "We believe an inclusive dialogue is needed to explore the use of animal drugs solely to improve performance, yet have no offsetting health benefits for the animals to which they are administered. This is particularly needed for those drugs that appear to adversely impact animal welfare, such as beta agonists."

Merck Animal Health issued a statement in response that cites the results of more than 30 controlled, randomized research trials showing no increase in death loss among cattle fed Zilmax. Further, Merck is sponsoring an extensive field evaluation program of Zilmax conducted by independent experts. Merck also said that the analysis in Loneragan’s research was based on observational data, rather than controlled, randomized experiments.

Merck removed Zilmax from the market in August of last year after major packing companies announced they would stop buying cattle fed the product. The last Zilmax-fed cattle were slaughtered in September. The company maintains a web page with additional information about Zilmax.

Loneragan, professor of food safety and public health in Texas Tech’s College of Agricultural Sciences and Natural Resources, said, "Beta agonists improve the efficiency of beef production and this improvement provides important societal benefits. The beta agonists approved by the U.S. Food and Drug Administration for use in cattle increase muscle growth and may reduce the amount of fat the cattle accumulates. This means the cattle convert more of the feed they eat into beef, and they do this more efficiently."

With the use of beta agonists, cattle require less feed and less water to produce the same amount of beef than if no beta agonists were used. Less land would be used to grow the crops used to feed the animals and, therefore, less fuel to produce the same amount of beef.
"However, through our extensive analysis, we found that the incidence of death among cattle administered beta agonists was 75 to 90 percent greater than cattle not administered the beta agonists," Loneragan said.

The researchers analyzed three datasets: one included information from randomized and controlled clinical trials of Optaflexx, while the other two were observational data on Zilmax. Analysis of those datasets indicated an association between beta agonist use and increased mortality rates among heavy cattle, particularly during periods of risk for heat stress or cold stress.

The findings were "based on observational information and we disagree with them," Merck said in its statement. "Using observational analyses where cattle are not randomized and where rigorous scientific procedures are not utilized, is not a respected scientific method to rigorously evaluate the safety and efficacy of any product," Merck said.

The FDA said it will review the new research data and add them to the agency's body of knowledge regarding Zilmax. The agency, which has deemed both drugs safe for animals and humans, can ask drug companies to make changes to product labels if it detects safety concerns.